1. Field of the Invention
The present invention relates to a curable composition including an aromatic nitrogen-containing heterocyclic azo dye, to a negative type color filter and to a method of producing the color filter.
2. Description of the Related Art
A pigment dispersion method is known as a method for producing a color filter to be used for a liquid crystal display device or a solid state image pickup device.
The pigment dispersion method is a method for producing a color filter by photolithography from colored radiosensitive compositions obtained by dispersing pigments in a variety of photosensitive compositions. In this method, obtained color filters are stable with respect to light and heat since pigments are used, and they are provided with sufficient positioning precision since patterning is carried out by photolithography. Thus the method has been widely used since it is suitable for producing a color filter for a high precision color display with a large size.
To produce such a color filter by the pigment dispersion method, a radiosensitive composition is applied to a substrate by a spin coater or a roll coater and dried to form a film, and the film is exposed to light and developed to obtain color pixels. These steps are repeated an appropriate number of times corresponding to the number of the hues, to obtain a color filter. Negative type photosensitive compositions containing photopolymerizable monomers and photopolymerization initiators together in alkali-soluble resins have been disclosed for use in the pigment dispersion method.
However, although further improved precision has recently been desired in a color filter for a solid state image pickup device, the resolution cannot be improved substantially by a conventional pigment dispersion method, and also, color irregularities are caused due to bulky particles of the pigment. Thus, such a conventional pigment dispersion method is unsuitable for uses where fine patterns are required, such as in a solid state image pickup device.
In order to achieve high image resolution, techniques in which dyes are used as the coloring materials have been investigated (see, for example, Japanese Patent Application Laid-open (JP-A) No. 6-75375). However, it has been found that a dye-containing curable composition has the following problems.
(1) Dyes are, in general, inferior to pigments in light fastness and heat resistance.
(2) It is difficult to obtain a liquid state curable composition having a desired spectrum since a conventional dye has a poor solubility in either an aqueous alkaline solution or an organic solvent (hereinafter, simply referred to as solvent in some cases).
(3) It is difficult to adjust the solubility (developing property) of cured parts and non-cured parts since most dyes interact with another component in the curable composition.
(4) A large quantity of a dye has to be added in the case where the molar extinction coefficient(ε) of the dye is low, and therefore, a content of other components such as polymerizable compounds (monomers), a binder, a photopolymerization initiator and the like have to be reduced in the curable composition, resulting in deterioration of the curability and the post-curing heat resistance of the composition and the developing property of (non) cured parts.
These problems have made it difficult to form a fine color pattern structured of a thin film for a highly precise color filter. Also, in the case of producing a color filter for a solid state image pickup device, unlike in the case of producing a semiconductor, the color pattern must be a film as thin as 1 μm or less. It is therefore necessary to add a large amount of dyes in a curable composition to obtain desired absorbance, with the result that the above problems arise.
Concerning highly durable dyes, it is usually demanded of colorants used for various uses to have in common the following properties. Specifically, it is necessary that these dyes have desirable absorbing characteristics for color reproducibility; are superior in durability under the environmental conditions under which the dyes are used, e.g., light fastness, heat resistance, moisture resistance, durability to acidic gases such as ozone, and chemical resistance durability with respect to sulfur dioxide and the like; and have a large molar extinction coefficient.
For example, phenol, naphthol or aniline is widely used as the coupling component of azo dyes, and azo dyes obtained by these coupling components and having a good hue are known. However, there is the problem that these dyes are inferior in light durability (see, for example, JP-A Nos. 59-30509 and 11-209673 and Japanese Patent No. 3020660). Also, several azo dyes containing pyridine or pyrazine as coupling components have been known (see, for example, JP-A No. 49-74718, EP23309, DE2513949, DE2832020 and DE2525505). However, at that time, the use of these dyes for color filters was unknown. Also, the azo dyes described in these documents have insufficient durability to light, heat, moisture and active gas in the environment. As to, particularly, magenta dyes, even the hue of these dyes are insufficient.